The present invention is directed to pilot-operated control valve systems and particularly to means for diverting pressurized fluid resulting from the supporting of a load for pilot operation of the system.
Large hydraulic control systems typically employ pilot operation of directional control valves for controlling the system. Such a pilot operation provides systems that require low effort on the part of the operator and thus enhances the ease of operation and control as well as permits remote location of main control valves from the operator compartment. Such systems, however, provide problems for portions of the system that lift and support large loads, such as implements or loads such as loaded implements.
Typically, the pilot control pressure is supplied by a pilot pump that is separate from the main fluid supply system. Such separate pump normally adds considerable expense to the machine.
With the prior art systems, should the engine fail and thus the pump for supplying the pilot fluid become inoperative while the implements or load of the system is in a raised position, no means is readily available for lowering the load. Such raised load or implement can become dangerous in the raised position should it suddenly fall because of rapid leak-out of the fluid in the cylinders.
It is therefore desirable to provide some means for controllably lowering the load or implements of such a machine should the pilot control pressure fail. Some such systems are known; however, they provide numerous disadvantages. One such system is shown in, for example, U.S. Pat. No. 3,620,129 issued to W. G. Fruehauf Nov. 16, 1971.